In the existing broadcast communication standards, LDPC coding, bit interleaving and constellation mapping are the most common coding and modulation modes. In different transmitting systems, the LDPC coding, the bit interleaving and the constellation mapping all require independent design and joint adjustment to achieve the best performance. Therefore, it is a technical problem in the art as regards how to form targeted bit interleaving for different LDPC code words by designing a constellation mapping mode with good performance through theoretical analysis and optimization so as to reduce the receiving threshold of a receiving end.